When you were a baby, you didn't have any teeth at all. Then as you
grew, your teeth started to come in. First one, then two - and finally,
twenty teeth in all!

But you won't keep these teeth forever. First one, then two, will wiggle
loose. Maybe you've lost some of your first teeth already. When the little
teeth come out and the big teeth come in, everyone can see - you're growing
up.